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Spin Couplings (spin + coupling)

Distribution by Scientific Domains

Chemistry	84%

Terms modified by Spin Couplings

spin coupling constant

Selected Abstracts

Unusual Mn,Mn Spin Coupling in the Polar Intermetallic Compounds CaMn2Sb2 and SrMn2Sb2.

CHEMINFORM, Issue 31 2006
Svilen Bobev
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

BINOL-3,3,-Triflone N,N -Dimethyl Phosphoramidites: Through-Space 19F,31P Spin,Spin Coupling with a Remarkable Dependency on Temperature and Solvent Internal Pressure

CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2008
Matthias Kruck
Abstract A combined computational and experimental study of the effects of solvent, temperature and stereochemistry on the magnitude of the through-space spin,spin coupling between 31P and 19F nuclei which are six-bonds apart is described. The reaction of 3-trifluoromethylsulfonyl-2,,2-dihydroxy-1,1,-binaphthalene (3-SO2CF3 -BINOL) with hexamethylphosphorous triamide (P(NMe2)3) generates a pair of N,N -dimethylphosphoramidites which are diastereomeric due to their differing relative configurations at the stereogenic phosphorous centre and the axially chiral (atropisomeric) BINOL unit. Through-space NMR coupling of the 31P and 19F nuclei of the phosphoramidite and sulfone is detected in one diastereomer only. In the analogous N,N -dimethylphosphoramidite generated from 3,3,-(SO2CF3)2 -BINOL only one of the diastereotopic trifluoromethylsulfone moieties couples with the 31P of the phosphoramidite. In both cases, the magnitude of the coupling is strongly modulated (up to 400,%) by solvent and temperature. A detailed DFT analysis of the response of the coupling to the orientation of the CF3 moiety with respect to the P-lone pair facilitates a confident assignment of the stereochemical identity of the pair of diastereomers. The analysis shows that the intriguing effects of environment on the magnitude of the coupling can be rationalised by a complex interplay of solvent internal pressure, molecular volume and thermal access to a wider conformational space. These phenomena suggest the possibility for the design of sensitive molecular probes for local environment that can be addressed via through-space NMR coupling. [source]

Crystal Structures and Magnetic Properties of Nitronyl Nitroxide Radicals

HELVETICA CHIMICA ACTA, Issue 4 2003
Alexander Zakrassov
The crystal structures and magnetic properties of the nitronyl nitroxide radicals 4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (1), 4,5-dihydro-2,4,4,5,5-pentamethyl-3-oxido(1H -imidazol-1-yloxyl) (2), 2-(4-chlorophenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (3), and 4,5-dihydro-2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (4) are reported. Compound 1 has two polymorphic forms: the , phase is monoclinic (P21/n space group), with a single molecule in the asymmetric unit, and the , phase is monoclinic (P21/c space group), with four molecules in the asymmetric unit. In the two polymorphs, the molecules are arranged in dimers formed by hydrogen bonds of the type CH,,,ON. The crystal structure of 3 contains layers of antiparallel ribbons of molecules. Compound 4 crystallizes with solvent molecules, and an intramolecular hydrogen bond is formed between the 2-OH group of the phenyl ring and the nitroxide O-atom. Compound 4 also loses the two O-atoms of the nitroxide moiety upon heating to 90°. Magnetic measurements showed that both , and , polymorphs of 1 exhibit antiferromagnetic coupling. The best fit to the experimental data was obtained using BleanyBower's singlet-triplet model (H=,2JSaSb): J=,11.2,K for the , phase and J=,15.0,K for the , phase. Compounds 3 and 4 show no evidence for spin coupling. [source]

Spin,spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethers

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007
Wallace S. Brey
Abstract The 19F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin,spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. Copyright © 2007 John Wiley & Sons, Ltd. [source]

NMR methods applied to anisotropic diffusion

MAGNETIC RESONANCE IN CHEMISTRY, Issue 13 2002
István Furó
Abstract The methodology of NMR experiments intended to measure anisotropic diffusion is reviewed. Experiments of this kind preferably require oriented samples and/or orientation-dependent spin coupling and/or magnetic field gradients in different directions. One strategy of diffusion experiments in anisotropic systems with broad NMR lines employs line narrowing techniques, thereby allowing for efficient gradient encoding/decoding. Depending on the nuclei, spin couplings and samples, the preferred methods vary from decoupling through echo techniques to magic angle sample orientation and spinning. Another avenue to efficient gradient encoding/decoding is through very strong magnetic field gradients. Either way, anisotropic diffusion reveals new structural features as illustrated by a few selected examples in liquid crystals and in biological tissues. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Local detection of Knight shift around quantum-Hall edge channels using resistively-detected NMR

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
S. Masubuchi
Abstract We develop a method for the observation of the Knight shift in nanometer-scale region in semiconductors using resistively detected nuclear magnetic resonance (RDNMR) in quantum Hall edge channels. Using a gate-induced decoupling of the hyperfine interaction between electron and nuclear spins, we obtain the RD-NMR spectra with and without the electron-nuclear spin coupling. By comparing these two NMR spectra, we obtain the values of the Knight shift for the nuclear spins polarized dynamically in the region between the relevant edge channels. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

BINOL-3,3,-Triflone N,N -Dimethyl Phosphoramidites: Through-Space 19F,31P Spin,Spin Coupling with a Remarkable Dependency on Temperature and Solvent Internal Pressure

A DFT and AIM analysis of the spin,spin couplings across the hydrogen bond in the 2-fluorobenzamide and related compounds

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2009
Ibon Alkorta
Abstract In 1975 a large number of coupling constants were measured in 2-fluorobenzamide labeled with 15N. Some of them were assigned to couplings through intramolecular NH···F hydrogen bonds (HBs). These couplings change dramatically when CDCl3 is replaced by DMSO- d6. In this theoretical paper we provide density functional theory (DFT) calculations that justify the existence of a weak HB in the absence of solvent, while solvents that act as HB acceptors break down the intramolecular hydrogen bond (IMHB) of 2-fluorobenzamide. Atoms in molecules (AIM) analyses and Steiner-Limbach plots were used to analyze the structure of the compounds. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Long-range JCH heteronuclear coupling constants in cyclopentane derivatives.

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2007
Part II
Abstract Here we report the detailed measurement of long-range heteronuclear spin,spin coupling constants, especially 2, 3JCH spin,spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X -CPMG-HSQMBC and the 2D-coupled gHSQC {1H- 13C} experiment Copyright © 2006 John Wiley & Sons, Ltd. [source]

29Si,13C spin,spin couplings over Si,O,Carom link

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2006
Jan Sýkora
Abstract 29Si,13C couplings were measured in para substituted silylated phenols, XC6H4OSiR1R2R3(X 2, CF3, Cl, F, H, CH3, CH3O). The SiR1R2R3 silyl groups included trimethylsilyl (Si(CH3)3, TMS), tert- butyldimethylsilyl (Si(CH3)2C(CH3)3, TBDMS), dimethylsilyl (SiH(CH3)2, DMS), and tert- butyldiphenylsilyl (Si(C6H5)2C(CH3)3, TBDPS). Previously developed (Si,C,Si)gHMQC methods and narrow 29Si lines allowed the determination of coupling constants over up to five bonds. Besides the number of intervening bonds between the silicon and carbon atoms, all the measurable couplings depend also on the nature of the substituents on the silicon. The two- and three-bond couplings are not affected by ring substitution in the para position. These properties render the 29Si,13C couplings suitable for line assignment in the spectra of silylated polyphenols. The experimental results are in reasonable agreement with theoretical calculations. The calculations show, in agreement with the data reported in the literature for couplings between other nuclei, that the two-bond and three-bond couplings, which are of similar magnitudes, are of opposite signs. If the signs of these geminal and vicinal couplings could be determined experimentally, they would greatly facilitate the line assignment. The four- and five-bond couplings are affected by the substituent X in a nontrivial manner. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Non-empirical calculations of NMR indirect carbon,carbon coupling constants.

MAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2004
Monocycloalkanes, Part
Abstract Carbon,carbon and carbon,hydrogen spin,spin coupling constants were calculated in the series of the first six monocycloalkanes using SOPPA and SOPPA(CCSD) methods, and very good agreement with the available experimental data was achieved, with the latter method showing slightly better results in most cases, at least in those involving calculations of J(C,C). Benchmark calculations of all possible 21 coupling constants J(C,C), J(C,H) and J(H,H) in chair cyclohexane revealed the importance of using the appropriate level of theory and adequate quality of the basis sets. Many unknown couplings in this series were predicted with high confidence and several interesting structural trends (hybridization effects, multipath coupling transmission mechanisms, hyperconjugative interactions) were elucidated and are discussed based on the present calculations of spin,spin couplings. Copyright © 2004 John Wiley & Sons, Ltd. [source]

NMR methods applied to anisotropic diffusion

Lactate isotopomer analysis by 1H NMR spectroscopy: Consideration of long-range nuclear spin,spin interactions

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2004
Steven G. Lloyd
Abstract Lactate is a key metabolite and its rates of cellular uptake and release, its production rates from glucose and glycogen, and its interconversion rate with pyruvate are important determinants of cellular energy production. If lactate precursors such as pyruvate and glucose are labeled appropriately with 13C, 1H NMR spectroscopy provides a means of quantifying lactate production from each source and allows measurement of all these rates within a single experiment. However, due to the multiplicities of the resonance lines (from nuclear spin,spin couplings) in lactate 13C isotopomers, the 1H NMR spectra were found to be more complex than expected, requiring determination of all spin,spin interactions in this anion. All such values were determined for lactate and its precursor pyruvate. The method was then applied to simultaneously measure the rates of exogenous lactate uptake and rates of release of glucose-, glycogen-, and pyruvate-derived lactate in the isolated perfused rat heart. Magn Reson Med 51:1279,1282, 2004. © 2004 Wiley-Liss, Inc. [source]